Process and plant for producing c2-c4 olefins from methanol and/or dimethyl ether with increased yield

ABSTRACT

A process and a plant for producing C 2 -C 4  olefins, in particular propylene, from an educt mixture containing steam as well as methanol vapor and/or dimethyl ether vapor. The educt mixture is reacted in at least one first reactor on a granular, form-selective zeolite catalyst to obtain a reaction mixture including low-molecular olefins and gasoline hydrocarbons, which in a first separating device is separated into a mixture rich in C 2 -C 4  olefins, a mixture rich in C 5+  gasoline hydrocarbons, and an aqueous phase, wherein the mixture rich in gasoline hydrocarbons is mixed with an inert medium, the mixture thus obtained is reacted in at least one second reactor on a granular zeolite catalyst to obtain a product mixture including C 2 -C 4  olefins, and this product mixture is recirculated to the first separating device, and wherein the mixture rich in C 5+  gasoline hydrocarbons is separated in a second separating device into a product stream containing C 5 -C 6  hydrocarbons and a product stream containing C 7+  hydrocarbons, before being supplied to the second reactor, and only the product stream containing C 7+  hydrocarbons is supplied to the second reactor, whereas the product stream containing C 5 -C 6  hydrocarbons together with the educt mixture is supplied to the at least one first reactor.

PRIORITY

This application claims the benefit of German Patent Application No. DE102005029399.9, filed Jun. 24, 2005, and International PatentApplication Serial No. PCT/EP2006/006065, filed Jun. 23, 2006, eachentitled “Process and Plant for Producing C₂-C₄ Olefins from Methanoland/or Dimethyl Ether with Increased Yield”, wherein each of theseapplications is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a process for producing C₂-C₄ olefins,in particular propylene, from an educt mixture containing steam as wellas methanol vapor and/or dimethyl ether vapor.

BACKGROUND OF THE INVENTION

For producing low-molecular C₂-C₄ olefins, in particular propylene, frommethanol and/or dimethyl ether, a multitude of processes are known tothose skilled in the art, which are usually based on the reaction of aneduct mixture containing steam as well as methanol vapor and/or dimethylether vapor on a form-selective zeolite catalyst.

DE 100 27 159 A1 discloses a process for producing propylene frommethanol, in which first a vapor mixture containing dimethyl ether isproduced from methanol vapor on a first catalyst, before the same ismixed with steam and is reacted in at least two sequentially operatedreactors with catalyst beds of form-selective zeolite to obtain aproduct mixture containing propylene. Subsequently, the product mixtureis processed in a separating device comprising several distillationcolumns, so that there is obtained a fraction rich in propylene with apropylene content of at least 95 vol-%, a fraction containinglow-molecular hydrocarbons, which is recirculated to the catalyst beds,and a fraction rich in gasoline hydrocarbons, which is removed from theprocess. What is, however, disadvantageous in this process is the lowyield of propylene, based on the total carbon content of the eductmixture, which among other things is due to the fact that the fractionrich in gasoline hydrocarbons is removed from the process.

From EP 0 882 692 B1 a process is known for producing C₂-C₃ olefins, inwhich a mixture of steam and methanol vapor and/or dimethyl ether vaporis reacted in a tubular reactor containing a zeolite catalyst at atemperature between 280 and 570° C. and a pressure between 0.1 and 0.9bar to obtain a product mixture rich in olefins, which subsequently isseparated in a separating device to obtain a C₂-C₄ olefin fraction witha propylene content of at least 40 wt-%, an aqueous fraction, a gaseousfraction, and a fraction containing C₅₊ gasoline hydrocarbons. While thethree first-mentioned fractions are withdrawn from the process, theproduct stream containing the C₅₊ gasoline hydrocarbons is mixed withwater, heated in a heater to a temperature of 380 to 700° C., andreacted to obtain C₂-C₄ olefins in a second reactor containing a zeolitecatalyst, before the reaction products are recirculated to theseparating device. The yields of C₂-C₃ olefins obtained with thisprocess, although higher than the yields obtained with the process knownfrom DE 100 27 159 A1, in which the fraction rich in gasolinehydrocarbons is removed from the process, likewise are in need ofimprovement. In addition, this process is known for its high costs, notleast because of the isothermal procedure and the necessary vacuumoperation in the tubular reactor.

What is needed is to provide a process for producing C₂-C₄ olefins, inparticular propylene, from an educt mixture containing steam as well asmethanol vapor and/or dimethyl ether vapor with a rather high yield.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a process for producing C₂-C₄olefins from an educt mixture containing steam and methanol vapor and/ordimethyl ether vapor. The process includes reactive the educt mixture inat least one first reactor on a granular, form-selective zeolitecatalyst to obtain a reaction mixture comprising low-molecular olefinsand gasoline hydrocarbons, and separating the reaction mixture in afirst separating device into a mixture rich in C₂-C₄ olefins, a mixturerich in C₅₊ gasoline hydrocarbons, and an aqueous phase. Furthermore, incertain embodiments, the process includes mixing the mixture rich ingasoline hydrocarbons with an inert medium and reacting the resultingmixture in at least one second reactor on a granular zeolite catalyst toobtain a product mixture comprising C₂-C₄ olefins and recirculating theproduct mixture to the first separating device. In addition, beforebeing supplied to the second reactor, the mixture rich in C₅₊ gasolinehydrocarbons can be separated in a second separating device into aproduct stream containing C₅-C₆ hydrocarbons and a product streamcontaining C₇, hydrocarbons and only the product stream containing C₇₊hydrocarbons is supplied to the second reactor, whereas the productstream containing C₅-C₆ hydrocarbons is supplied to the at least onefirst reactor together with the educt mixture.

An additional aspect of the invention relates to a plant for producingC₂-C₄ olefins, in particular propylene, from an educt mixture containingsteam as well as methanol vapor and/or dimethyl ether vapor. The planttypically includes at least one first reactor and at least one secondreactor, each of which contains a granular form-selective zeolitecatalyst. The plant further includes a first separating device forseparating the reaction mixture obtained in the first reactor and asecond separating device which is adapted to separate a mixture rich inC₅₊ gasoline hydrocarbons into a product stream containing C₅-C₆hydrocarbons and a product stream containing C₇₊ hydrocarbons beforesupplying the same to the second reactor. The plant also includes areturn line which leads from the second reactor to the first separatingdevice.

The above summary of the present invention is not intended to describeeach discussed embodiment of the present invention. This is the purposeof the figures and the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWING

The invention may be more completely understood in connection with thefollowing drawing, in which:

FIG. 1 schematically shows a plant which can be used for performing theprocess of the invention.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawing, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for producing C₂-C₄ olefins,in particular propylene, from an educt mixture containing steam as wellas methanol vapor and/or dimethyl ether vapor, in which the eductmixture is reacted in at least one first reactor on a granular,form-selective zeolite catalyst to obtain a reaction mixture comprisinglow-molecular olefins and gasoline hydrocarbons, which in a firstseparating device is separated into a mixture rich in C₂-C₄ olefins, amixture rich in C₅₊ gasoline hydrocarbons, and an aqueous phase, whereinthe mixture rich in gasoline hydrocarbons is mixed with an inert medium,the mixture thus obtained is reacted in at least one second reactor on agranular zeolite catalyst to obtain a product mixture comprising C₂-C₄olefins, and this product mixture is recirculated to the firstseparating device. The present invention furthermore relates to a plantsuitable for performing the process.

In accordance with the present invention, the yield of C₂-C₄ olefins ina process for producing C₂-C₄ olefins, in particular propylene, from aneduct mixture containing steam as well as methanol vapor and/or dimethylether vapor is increased significantly without increasing the operatingcosts, when the fraction containing C₅₊ gasoline hydrocarbons, which inthe first separating device was separated from the reaction mixtureobtained upon reaction of the educt mixture in the first reactor, isfirst of all separated in a second separating device into a productstream comprising C₅-C₆hydrocarbons as well as a product streamcomprising C₇₊ hydrocarbons, and only the product stream containing theC₇₊ hydrocarbons is reacted in the second reactor, whereas the productstream containing the C₅-C₆ hydrocarbons together with the educt mixtureis supplied to the at least one first reactor and is again reacted thereto obtain low-molecular olefins. Both the product stream containingC₅-C₆ hydrocarbons and the product stream containing C₇₊ hydrocarbonscontains unexpectedly high amounts of compounds which can be reacted ona form-selective zeolite catalyst to obtain C₂-C₄ olefins. While thelast-mentioned fraction of C₇₊ hydrocarbons includes significant amountsof aromatics, which react with methanol and/or dimethyl ether by formingalkylaromatic compounds, and therefore cannot be reacted together withthe educt mixture containing methanol and/or dimethyl ether, thefirst-mentioned fraction of C₅-C₆ hydrocarbons is substantially freefrom aromatics and therefore can be used in the first reactor without arisk of undesired side reactions.

In the second separating device, a product stream containing C₇+.hydrocarbons, which comprises 10 to 30 wt-% of C₇₊ paraffins, 40 to 70wt-% of aromatics, 5 to 20 wt-% of naphthenes, 5 to 25 wt-% of C₇₊olefins as well as less than 20 wt-% of C6-hydrocarbons, is preferablyseparated from the mixture rich in C₅₊ gasoline hydrocarbons, as thesecompositions have a high content of compounds which can be reacted on azeolite catalyst to obtain C₂-C₄ olefins and in particular propylene.Particularly good results are obtained when the C₇₊ product streamseparated in the second separating device contains 15 to 25 wt-% of C₇₊paraffins, 40 to 50 wt-% of aromatics, 15 to 20 wt-% of naphthenes, 15to 25 wt-% of C₇₊ olefins as well as less than 10 wt-% ofC6-hydrocarbons. Quite particularly preferably, the content ofC6-hydrocarbons, i.e. hydrocarbons with a chain length of 6 C atoms orless, in the C₇₊ product stream is less than 5 wt-%.

In accordance with the invention, it is possible to separate in thesecond separating device a product stream containing C₅-C₆ hydrocarbons,which contains less than 5 wt-% of aromatics, preferably less than 2.5wt-% of aromatics, and particularly preferably less than 1 wt-% ofaromatics. These compositions also have a high content of compoundswhich can be reacted on a zeolite catalyst to obtain C₂-C₄ olefins andin particular propylene. In addition, the low content of aromaticsensures that in the subsequent reaction of the C₅-C₆ product stream inthe first reactor no undesired side reactions, in particular noalkylation reactions with methanol, do occur.

The second separating device can be designed in any way known to thoseskilled in the art, if it is adapted to separate a mixture rich in C₅₊gasoline hydrocarbons into a product stream containing C₅-C₆hydrocarbons and a product stream containing C₇₊ hydrocarbons. Merely byway of example, reference should be made to separating devices operatingby distillation, by adsorption, thermally or by means of membranes,particularly good results being obtained by means of distillationcolumns.

As inert medium to be supplied to the product stream containing C₇₊hydrocarbons, which was formed in the second separating device, water,nitrogen and/or butane turned out to be particularly useful, water beingparticularly preferred for this purpose.

In accordance with the invention, the educt mixture supplied to thefirst reactor can contain 0 to 100 wt-% of methanol and 100 to 0 wt-% ofdimethyl ether in addition to steam, based on its steam-free content.Gas mixtures containing methanol and or dimethyl ether can for instancebe produced in a manner known per se by partial conversion of methanolon a granular alumina catalyst, the reaction preferably being performedat a temperature between 200 and 350° C.

Preferably, the first reactor constitutes a fixed bed reactor, tubularreactor, stationary fluidized-bed reactor or circulating fluidized-bedreactor. In the second case, the reactor preferably includes a pluralityof axially arranged tubes, which for instance have a length between 1 mand 5 m as well as an inside diameter of 20 mm to 50 mm.

To achieve a rather high conversion of the educt mixture, the same ispassed through two or more sequentially operated first reactors, inaccordance with a particular embodiment of the present invention. Forthis embodiment, in particular more than two, preferably three,series-connected fixed bed reactors each with a form-selective zeolitecatalyst turned out to be particularly useful, part of the educt mixturefrom the prereactor being introduced into the first fixed bed reactorand the product mixture from the fixed bed reactor upstream of eachfurther reactor together with a partial stream of the educt mixture fromthe prereactor being introduced into each further fixed bed reactor.

Similar conversions of the educt mixture are obtained when as analternative to the aforementioned embodiment the educt mixture is passedonly through a first reactor, in which at least two sequentiallyoperated catalyst stages are provided. In this case, the individualcatalyst stages preferably are arranged one below the other and aretraversed by the educt mixture from the top to the bottom. Here as well,the educt mixture is distributed from the prereactor to the individualcatalyst stages.

In principle, all zeolite catalysts known to those skilled in the art assuitable for the conversion of methanol and/or dimethyl ether into C₂-C₄olefins can be used in the at least one first reactor, whereinalumosilicate zeolite of the pentasile type and particularly preferablyZSM-5 turned out to be particularly useful. For optimizing the yield, itis furthermore preferred to supply at least one inert stream,particularly preferably steam, and at least one stream containinghydrocarbons, to the reactor, i.e. the first reactor or the firstreactor stage.

In order to decrease the operating costs of the process, it is proposedin accordance with a development of the invention to perform theconversion in the at least one first reactor and/or in the at least onesecond reactor adiabatically. Alternatively, an isothermal procedure ispossible, although less preferred, in the aforementioned reactors, whichas compared to the adiabatic procedure, would, however, lead to higherprocess costs.

Good yields in the at least one first reactor are obtained inparticular, when an educt mixture with a weight ratio of water tomethanol equivalent of 0.25:1 to 6:1 is supplied thereto. If the reactorcomprises a plurality of catalyst stages, this ratio applies to theinlet of each catalyst stage. According to equation 2 withCH₃OH→CH₃—O—CH₃+H₂O, one “methanol equivalent” corresponds to half amole of dimethyl ether (DME). In addition, the educt mixture ispreferably reacted in the first reactor at a temperature of 300 to 600°C. and/or at a pressure of 0.5 to 5 bar(a).

For separating the reaction mixture withdrawn from the first reactor,there can be used any separating device known to those skilled in theart, which can be used for separating a mixture rich in C₂-C₄ olefinsfrom a mixture rich in C₅₊ gasoline hydrocarbons, for instanceseparating devices operating by distillation, by adsorption, thermallyor by means of membranes. Particularly good results are obtained whenthe first separating device constitutes a cooling device and thereaction mixture withdrawn from the first reactor is cooled therein to atemperature of 10 to 80° C.

In accordance with a further preferred embodiment of the presentinvention, the mixture rich in C₂-C₄ olefins withdrawn from the firstseparating device is supplied to a third separating device, in which theaforementioned mixture is separated into a C₄-C₅ olefin stream and a C³⁻olefin stream. This provides for the recirculation of the C₄-C₅ olefinstream to the first reactor, whereby the total yield of the process canfurther be increased. From the C³⁻ olefin stream, propylene can easilybe recovered, with a high purity for instance by distillation.Preferably, the olefins left upon separation of propylene from the C³⁻olefin stream are also recirculated to the first reactor.

In the second reactor, the same catalysts as in the first reactor can beused in principle, alumosilicate zeolite of the pentasile type and inparticular ZSM-5 being preferred. In particular, good yields areobtained in the second reactor when a mixture with a water/hydrocarbonratio of 0.1:1 to 3:1 and preferably at least 1:1 is supplied thereto.In addition, the product stream in the second reactor is preferablyreacted at a temperature of 380 to 700° C. and particularly preferablyof 400 to 600° C. and/or preferably at a pressure of 0.2 to 5 bar(a) andparticularly preferably of 1.0 to 2.5 bar(a).

Another aspect of the present invention is a plant for producing C₂-C₄olefins, in particular propylene, from an educt mixture containing steamas well as methanol vapor and/or dimethyl ether vapor, which plant isparticularly useful for performing the processes described herein. Inaccordance with the invention, the plant comprises at least one firstreactor and at least one second reactor, both reactors containing each agranular form-selective zeolite catalyst, as well as a first separatingdevice for separating the reaction mixture obtained in the firstreactor, wherein the plant furthermore includes a second separatingdevice which is adapted to separate a mixture rich in C₅₊ gasolinehydrocarbons into a product stream containing C₅-C₆ hydrocarbons and aproduct stream containing C₇₊ hydrocarbons before supplying the same toa second reactor, and wherein a return line leads from the secondreactor to the first separating device.

In accordance with an embodiment of the present invention, a thirdseparating device for separating the mixture rich in C₂-C₄ olefins,which was withdrawn from the first separating device, into a C₄-C₅olefin stream and a C³⁻ olefin stream is provided downstream of thefirst separating device, wherein the third separating device comprisesat least one distillation column.

In another embodiment of the invention it is proposed to provide in theplant a return line leading from the third separating device to thefirst reactor, in order to recirculate the mixture rich in C₄-C₅olefins, which was withdrawn from the third separating device, into thefirst reactor.

The plant as shown in FIG. 1 comprises a first reactor 1 and a secondreactor 2, each of which contains a catalyst on the basis ofform-selective zeolite, preferably an alumosilicate zeolite of thepentasile type and particularly preferably ZSM-5. While the firstreactor 1 preferably constitutes a fixed bed reactor, tubular reactor,stationary fluidized-bed reactor or circulating fluidized-bed reactor,the catalyst in the second reactor 2 preferably is arranged as fixedbed. Furthermore, the plant comprises a first separating device 3designed as cooler as well as a second separating device 4.

During operation of the plant, methanol supplied via the methanol supplyline 5 is heated in a heat exchanger (not shown) to a temperature ofpreferably 200 to 350° C. and is evaporated thereby, before the methanolvapor is at least partly reacted in the prereactor 6 on a suitabledehydrating catalyst, e.g alumina, to obtain dimethyl ether and water.Via gas line 8, steam is supplied to the methanol/dimethyl ether mixturewithdrawn from the prereactor via line 7, and the mixture thus obtainedis introduced into the first reactor 1. Preferably, the inlettemperature of the educt mixture into the first reactor 1 is between 350and 500° C., the weight ratio of water to methanol equivalent in theeduct mixture is between 0.25:1 and 6:1, and the pressure in the firstreactor 1 is between 0.5 and 5.0 bar(a). Inside the catalyst layers ofthe first reactor, the temperatures preferably lie in the range between300 and 600° C.

As an alternative to the one-stage configuration of the first reactor 1as shown in FIG. 1, the same can also consist of two or moresequentially operated reaction stages, which can both constituteseparately designed reactors and catalyst beds disposed one above theother in one reactor. In this case, the product from the prereactor 6 isdistributed on the individual stages, whereas all other inlet streamsare completely introduced into the first reaction stage. Furthermore, itis also possible to exclusively use methanol or dimethyl ether incombination with steam as educt in the first reactor 1 instead of asteam/methanol/dimethyl ether mixture.

Via line 9, the reaction mixture formed in the first reactor 1, whichmainly consists of C₂-C₄ olefins, C₅₊ gasoline hydrocarbons and steam,is withdrawn from the first reactor 1 and supplied to the firstseparating device 3, in which the reaction mixture is cooled to atemperature between 10 and 80° C., so that a condensate rich in water,an organic liquid phase rich in C₅₊ gasoline hydrocarbons, and a gasphase substantially consisting of C₂-C₄ olefins are obtained.

From the first separating device 3, the fraction rich in C₂-C₄ olefinsis supplied via line 10 to a third separating device 11, in which it isseparated into a C₄-C₅ olefin stream and a C³⁻ olefin stream. While thefirst-mentioned olefin stream is recirculated to the first reactor 1 viathe return line 12 and the methanol/dimethyl ether discharge line 7,propylene and propane are separated from the C³⁻ olefin stream via afurther separating device (not shown), and the residual C²⁻ stream freefrom propylene is recirculated to the first reactor via line 15. Thefurther purification of the propylene separated from the C³⁻ olefinstream can be achieved by means of processes known from the prior art.

Via line 13, the organic phase obtained in the first separating device3, which substantially consists of C₅₊ gasoline hydrocarbons, isintroduced into the second separating device 4, which constitutes adistillation column and in which this phase is separated into a C₅-C₆hydrocarbon stream and a C₇₊ hydrocarbon stream. The first-mentionedhydrocarbon stream is recirculated to the first reactor 1 via the returnline 12′ and the methanol/dimethyl ether discharge line 7, whereas theC₇₊ hydrocarbon stream is first passed through a heater (not shown), inwhich the mixture of C₇₊ hydrocarbons and water is heated to atemperature of preferably 380 to 600° C., via line 13′, to which waterwithdrawn as liquid condensate from the first separating device 3 issupplied via line 14, and is subsequently introduced into the secondreactor 2, in which the aforementioned mixture is reacted on a granularzeolite catalyst to obtain a product mixture comprising C₂-C₄ olefins.Via return line 12″, this product mixture is withdrawn from the secondreactor 2 and recirculated to the first separating device 3.

To avoid too high concentrations of inert substances in the processloop, a small amount of the C₂-C₄ olefins, the C₅-C₆ hydrocarbons andthe C₇₊ hydrocarbons is continuously discharged from the process circuit(not shown).

The invention will be explained below with reference to an exampledemonstrating the invention, but not limiting the same.

Example 1

In a plant such as shown in FIG. 1, 2.23 kg/h of a mixture of 8.7 wt-%of methanol vapor, 32.9 wt-% of dimethyl ether vapor and 58.3 wt-% ofsteam were supplied to the first reactor 1 via lines 5, 7, 8; 0.75 kg/hof the C₄-C₅ olefin stream withdrawn from the third separating devicevia lines 12, 7; 0.13 kg/h of ethylene via lines 15, 7, and via lines12′, 7; 0.18 kg/h of the C₅-C₆ hydrocarbon stream withdrawn from thesecond separating device, the inlet temperature of the mixtureintroduced into reactor 1 being 459° C. and the pressure at the inlet ofreactor 1 being 2.15 bar(a).

Via line 9, the reaction mixture was withdrawn from reactor 1 andintroduced into the first separating device 3 constituting a cooler, inwhich the reaction mixture was cooled to 24° C. 0.33 kg/h of a fractionrich in C₅₊ gasoline hydrocarbons, based on 1 kg of catalyst in thefirst reactor 1, were withdrawn from the bottom of the separating device3 and were separated in the second separating device 4 into a productstream containing C₅-C₆ hydrocarbons and a product stream containing C₇₊hydrocarbons, wherein the product stream containing the C₇₊ hydrocarbonshad the following composition:

18.5 wt-% of C₇₊ paraffins,

42.4 wt-% of aromatics,

18.7 wt-% of naphthenes,

19.2 wt-% of C₇₊ olefins, and

less than 0.3 wt-% of C₆ hydrocarbons and the product stream containingC₅-C₆ hydrocarbons had the following composition:

32.6 wt-% of C⁷⁻ paraffins,

0.2 wt-% of aromatics,

14.3 wt-% of naphthenes, and

52.9 wt-% of C⁷⁻ olefins.

While the product stream containing C₅-C₆ hydrocarbons was recirculatedto the first reactor 1 via lines 12′, 7, the product stream containingC₇₊ hydrocarbons with a mass flow rate of 3 kg/h was mixed with 1.5 kg/hof steam, based on one kilogram of catalyst in the second reactor 2, themixture thus obtained was heated and with an inlet temperature of about480° C. introduced into the second reactor 2, which was operated at apressure of 1.3 bar(a). The product withdrawn from reactor 2 wasrecirculated to the first separating device 3 via line 12″ with a massflow rate of 0.095 kg/h.

In addition, a mixture rich in C₂-C₄ olefins was withdrawn from thefirst separating device and supplied via line 10 to a third separatingdevice 11, in which this stream was separated into a C₄-C₅ olefin streamand a C3-olefin stream. From the C3-olefin stream, propylene wasrecovered with a yield of 69.3%.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the present specification. Theclaims are intended to cover such modifications and devices.

The above specification provides a complete description of the structureand use of the invention. Since many of the embodiments of the inventioncan be made without parting from the spirit and scope of the invention,the invention resides in the claims.

1-18. (canceled)
 19. A process for producing C₂-C₄ olefins from an eductmixture containing steam and methanol vapor and/or dimethyl ether vapor,the process comprising: (i) reacting the educt mixture in at least onefirst reactor on a granular, form-selective zeolite catalyst to obtain areaction mixture comprising low-molecular olefins and gasolinehydrocarbons; (ii) separating the reaction mixture in a first separatingdevice into a mixture rich in C₂-C₄ olefins, a mixture rich in C₅₊gasoline hydrocarbons, and an aqueous phase; (iii) mixing the mixturerich in gasoline hydrocarbons with an inert medium and reacting theresulting mixture in at least one second reactor on a granular zeolitecatalyst to obtain a product mixture comprising C₂-C₄ olefins; and (iv)recirculating the product mixture to the first separating device; (v)wherein before being supplied to the second reactor, the mixture rich inC₅₊ gasoline hydrocarbons is separated in a second separating deviceinto a product stream containing C₅-C₆ hydrocarbons and a product streamcontaining C₇₊ hydrocarbons and only the product stream containing C₇₊hydrocarbons is supplied to the second reactor, whereas the productstream containing C₅-C₆ hydrocarbons is supplied to the at least onefirst reactor together with the educt mixture.
 20. The process of claim19, where the product stream containing C₇₊ hydrocarbons, which wasseparated in the second separating device, contains 10 to 30 wt-% of C₇₊paraffins, 40 to 70 wt-% of aromatics, 5 to 20 wt-% of naphthenes, 5 to25 wt-% of C₇₊ olefins as well as less than 20 wt-% of C6-hydrocarbons21. The process of claim 19, where the product stream containing C₇₊hydrocarbons contains 15 to 25 wt-% of C₇₊ paraffins, 40 to 50 wt-% ofaromatics, 15 to 20 wt-% of naphthenes, 15 to 25 wt-% of C₇₊ olefins andless than 5 wt-% of C⁶⁻ hydrocarbons.
 22. The process of claim 19, wherethe product stream containing C₅-C₆ hydrocarbons, which was separated inthe second separating device, contains less than 5 wt-% of aromatics.23. The process of claim 19, where the product stream containing C₅-C₆hydrocarbons, which was separated in the second separating device,contains less than 2.5 wt-% of aromatics.
 24. The process of claim 19,where the product stream containing C₅-C₆ hydrocarbons, which wasseparated in the second separating device, contains less than 1 wt-% ofaromatics.
 25. The process of claim 19, where the second separatingdevice comprises a distillation column.
 26. The process of claim 19,where before being supplied to the second reactor, the mixture rich inC₇₊ gasoline hydrocarbons is mixed with water, nitrogen and/or butane asinert medium.
 27. The process of claim 19, where the at least one firstreactor comprises a fixed bed reactor, tubular reactor, stationaryfluidized-bed reactor or circulating fluidized-bed reactor.
 28. Theprocess of claim 19, where the first reactor comprises two or moresequentially operated reactors or at least two sequentially operatedcatalyst stages.
 29. The process of claim 19, where the catalyst in thefirst reactor or second reactor is an alumosilicate-zeolite of thepentasile type.
 30. The process of claim 29, where the catalyst isZSM-5.
 31. The process of claim 19, where the reaction in the at leastone first reactor or in the at least one second reactor is performedadiabatically.
 32. The process of claim 19, where the weight ratio ofwater to methanol equivalent, based on all methanol inlet streams, ofthe educt mixture supplied to the first reactor is adjusted to 0.25:1 to6:1, and the educt mixture is reacted in the first reactor at atemperature of 300 to 600° C. and/or at a pressure of 0.5 to 5 bar(a).33. The process of claim 19, where the first separating device is acooling device in which the reaction mixture is cooled to a temperatureof 10 to 80° C.
 34. The process of claim 19, where the mixture rich inC₂-C₄ olefins, which was obtained in the first separating device, issupplied to a third separating device in which the mixture is separatedinto a C₄-C₅ olefin stream and a C³⁻ olefin stream.
 35. The process ofclaim 34, where the C₄-C₅ olefin stream is recirculated to the firstreactor.
 36. The process of claim 35, where propylene is separated fromthe C³⁻ olefin stream and the remaining olefins are recirculated to thefirst reactor.
 37. The process of claim 19, where the water/hydrocarbonratio of the product stream supplied to the second reactor is adjustedto 0.1:1 to 3:1, and the product stream in the second reactor is reactedat a temperature of 380 to 700° C. and at a pressure of 0.2 to 5 bar(a).38. The process of claim 19, where the water/hydrocarbon ratio of theproduct stream supplied to the second reactor is adjusted to at least1:1, and the product stream in the second reactor is reacted at atemperature of 400 to 600° C. and at a pressure of 1.0 to 2.5 bar(a).39. A plant for producing C₂-C₄ olefins, in particular propylene, froman educt mixture containing steam as well as methanol vapor and/ordimethyl ether vapor, comprising: (i) at least one first reactor and atleast one second reactor, each of which contains a granularform-selective zeolite catalyst; (ii) a first separating device forseparating the reaction mixture obtained in the first reactor; (iii) asecond separating device which is adapted to separate a mixture rich inC₅₊ gasoline hydrocarbons into a product stream containing C₅-C₆hydrocarbons and a product stream containing C₇₊ hydrocarbons beforesupplying the same to the second reactor; and (iv) a return line whichleads from the second reactor to the first separating device.
 40. Theplant of claim 39, further comprising a third separating devicedownstream of the first separating device.
 41. The plant of claim 40,where the third separating device comprises at least one distillationcolumn.
 42. The plant of claim 39, further comprising a return lineleading from the third separating device to the first reactor.